JPS6075397A - Treatment of waste water - Google Patents

Abstract

PURPOSE:To remove simultaneously BOD and nitrogen compd. in waste water in a way as to economize resources by using a gravity downflow type contact oxidation method and maintaining respectively adequately the amt. of dissolved oxygen in the waste water in downflow water ways in respective stages for denitrification and nitrification. CONSTITUTION:Waste water contg. BOD material and nitrogen compd. is treated by a gravity downflow type contact oxidation method. A region where the dissolved oxygen in the waste water is <=1ppm is provided in the downflow water way of the denitrification stage in said stage. The dissolved oxygen in the waste water in the downflow water way of the nitrification stage is maintained at >=1ppm. The BOD and nitrogen compd. in the waste water are removed efficiently and simultaneously in this method simply by running downward the waste water without using power for the purpose of aeration and stirring. Maintenance and control are easy and the cost of the power for operation is low.

Description

[Detailed Description of the Invention] Wastewater containing elementary compounds is introduced into a waterway incorporating a filler, and power is applied to agitate the wastewater to bring it into contact with the above-mentioned light tank, aerate to supply oxygen, etc. The present invention relates to a resource-saving, energy-saving, inexpensive, and novel wastewater treatment method that uses a gravity-flow type catalytic oxidation method to treat wastewater at the end of its life.

Circulating nitrification and denitrification method using activated sludge method is a conventional method to remove BOD substances and nitrogen compounds that are a source of pollution in domestic wastewater, industrial wastewater, river, lake water, etc. using biochemical technology. This is due to the complexity of the treatment mechanism, the need for sludge treatment in the activated sludge method, and the need for advanced maintenance and management techniques such as adjusting the amount of oxygen and aeration, as well as the agitation of the aeration tank and the aeration of the oxygen supply tank. There are problems such as excessive power costs and high equipment costs. Also,
Conventionally, attempts have been made to incorporate a filler into the aeration tank and perform a cyclic nitrification and denitrification method using a contact aeration method, but in this case, although sludge treatment is easier in terms of maintenance and management, it is difficult to agitate the aeration tank, [Aerated air in the oxygen supply tank] 10) It has many problems, such as the need for adjustments, etc., and the power required for these is excessive, resulting in high equipment costs.

The present invention solves the above-mentioned problems of the prior art, can simultaneously remove BOD substances and nitrogen compounds from wastewater, and is easy to maintain and has low operating power costs, making it much cheaper than conventional methods. The aim is to provide a resource-saving and energy-saving wastewater treatment method. That is, the gist of the present invention is to introduce wastewater containing BOD substances and nitrogen compounds into a waterway incorporating a filler and allow it to flow down, and then mix the flowing water from the end of the waterway with the wastewater to contain the wastewater. In order to simultaneously remove BOD substances and nitrogen compounds in the wastewater by recirculating it to the introduction part of the waterway and forming a denitrification process and a nitrification process in the waterway, the filler and wastewater in the treatment process are A gravity-flow type catalytic oxidation method is used without using power for stirring the tank that contacts the water and aeration of the tank that supplies oxygen.
In the drainage waterway of the denitrification process in the gravity flow type catalytic oxidation process, an area is provided where the dissolved oxygen in the wastewater is less than 1 PPm. A wastewater treatment method is characterized in that the treatment is performed while maintaining dissolved oxygen at IPPm or higher.

The wastewater treatment method of the present invention is carried out as follows, as shown in an example of the treatment steps of the method of the present invention in FIG.

(1) Raw wastewater containing BOD substances and nitrogen compounds is first mixed with circulating liquid circulated from the nitrification process in the later stage of the gravity flow type catalytic oxidation process in the mixing process shown in FIG.

(2) The mixed solution obtained above is introduced into the denitrification step in the first stage of the gravity flow type catalytic oxidation step shown in FIG. In the denitrification process, while the mixed liquid flows down the waterway incorporating the filler, the oxidized nitrogen ( , mainly nitrate nitrogen) to nitrogen gas. At this time, the BOD substance in the raw wastewater is used as an organic carbon source (hydrogen donor) necessary for reduction and denitrification, and BOD is removed at the same time as denitrification. The basic reaction formula is as shown in (Formula 1) below: 2No; + IOH-* N,, ↑+4H20+
20H-... (1 formula) (3) The treated water from the above denitrification process is then introduced into the latter stage nitrification process in the gravity flow type catalytic oxidation process shown in Figure 1, and is added to the raw wastewater. The existing ammonia nitrogen is oxidized to oxidized nitrogen (mainly nitrate nitrogen) by the action of nitrifying bacteria that adhere to the surface of the filler by flowing wastewater into the waterway that incorporates the filler, and then BOD that still remains after the denitrification process is removed. The basic reaction formula is shown in (2) below: (4) The treated water from the above nitrification process is then led to the pumping process shown in Figure 1, and most of it is pumped through the circulation pump (1).
) is circulated to the mixing process with raw wastewater and mixed with raw wastewater.

That is, most of the oxidized nitrogen in the water treated in the nitrification process is introduced into the denitrification process (2) through the mixing tank together with the circulating liquid. The remainder flows out from the pumping process.

(5) The effluent from the above pumping step is introduced into the final settling step shown in FIG. 1, where suspended solids are settled and the supernatant water is discharged as treated water.

That is, the wastewater treatment method of the present invention reduces BOD in raw wastewater.
For the removal of substances and nitrogen compounds, this method uses BOD in the raw wastewater as a hydrogen donor and performs denitrification treatment to remove a large amount of nitrogen compounds, which was not necessary in conventional methods for denitrification treatment. There is no need for an alkaline agent9.Furthermore, the denitrification and nitrification processes in the gravity flow catalytic oxidation process do not require power for stirring and oxygen supply, making maintenance easy and reducing equipment and operating costs. It becomes an inexpensive system.

The raw wastewater and the denitrification process and nitrification process in the gravity flow type catalytic oxidation process in the treatment method of the present invention will be explained in more detail. When the effluent water from the nitrification process is recycled, the oxidized nitrogen in the recycled water is reduced to nitrogen gas, and the nitrogen compounds are removed. The content of both must be at least BOD/N==2 (weight ratio) or higher. If the content ratio is smaller than this value, the efficiency of the reduction reaction of oxidized nitrogen to nitrogen gas in the denitrification step decreases, which is not preferable. Therefore, when the content ratio is less than 2, it is necessary to separately add an organic compound such as methanol as an organic carbon source (hydrogen donor) in order to increase the denitrification effect 4. Other ingredients include:
When carrying out microbial treatment, it is necessary to contain approximately 1 moat of phosphorus per BOD.

The basic requirements for the filler to be incorporated into waterways during the denitrification process are chemically inert materials that have a high ability to maintain biofilm formation and do not prevent water from becoming muddy.
In the present invention, in particular, a plurality of plates made of plastic and having a corrugated pattern on the narrow side are stacked in parallel at regular intervals to obtain a specific surface area of 30 to 200 rr. /rri', a space ratio of about 95 to 99% is preferable, and is suitable for efficient and stable BOD removal and denitrification treatment. In other words, below 30 m"/z, the biofilm area involved in BOD removal and denitrification is insufficient, resulting in poor treatment efficiency; while above 200 m"/m, the biofilm area is sufficient, but the structure of the filler In addition, there is a risk that the flow of water may be obstructed by the formation of biofilm, which is problematic and undesirable for stable BOD removal and denitrification treatment.

In the waterway, the water flow velocity of the wastewater that comes into contact with the biofilm on the filler is set in the range of 0.1 to 30 m/min. In other words, if the water flow rate is less than 0.1 m 7 minutes, the water flow will be poor and the contact efficiency between wastewater and biofilm will be reduced, making it impossible to obtain sufficient performance for BOD removal and denitrification treatment.
Since the shearing force of the water flow on the biofilm is small, the biofilm may thicken and impede the flow of water, which is undesirable. On the other hand, if the water flow rate is 30 m/min or more, the shearing force on the biofilm becomes large, making it difficult to form a sufficient biofilm and reducing the BO
The performance of D removal and denitrification treatment deteriorates.

In addition, regarding the amount of filler used in the denitrification process, the amount of oxidized nitrogen flowing into the denitrification process, the amount of oxidized nitrogen, the surface area load of the filler (per 1 m2 of surface area of the filler),
It is set based on the relationship with the amount of oxidized nitrogen in wastewater that flows in per day.

On the other hand, the surface area loading of the oxidized nitrogen content is usually 0.0
2-10g r/rl? - Set to day range. In other words, for the oxidized nitrogen content and surface area load, 0.02
flr//rl?・Denitrification treatment performance can be obtained sufficiently at less than 1 day, but the equipment becomes too large and the overall efficiency deteriorates, resulting in L Ofr/n?・Denitrification performance deteriorates on Nitori, and both are problematic and undesirable. The above oxidized nitrogen load is calculated using the following formula assuming that all nitrogen compounds in the raw wastewater are oxidized to oxidized nitrogen.

Enemy nitrogen load = Nitrogen concentration in raw wastewater x raw wastewater volume Furthermore, in order to perform denitrification treatment efficiently, dissolved oxygen in the wastewater in the drainage waterway of the denitrification process is IPP.
It is important to provide (that is, exist) a region where the number is less than or equal to m. Further, it is preferable to carry out the treatment at a pH of about 6 to 9.

Next, in the nitrification process shown in Figure 1, the ammonia nitrogen present in the raw wastewater is oxidized to 1 point nitrogen oxide, and the BOD still remaining from the previous denitrification process is removed. The filler incorporated into the process channel is substantially the same in terms of basic requirements as the filler incorporated into the denitrification process described above. However, the specific surface area is 50 to 300 rn'
/+rI'', and the void ratio is preferably about 95 to 99%, which is suitable for efficient and stable oxidation of ammonia nitrogen and removal of BOD.

Furthermore, the water flow rate of the wastewater that comes into contact with the biofilm on the filler in the water channel may be the same as the water flow rate shown in the denitrification step described above.

In addition, regarding the amount of filler used in the nitrification process, the amount of ammonia nitrogen in the raw wastewater and the surface area load of the ammonia nitrogen filler (the amount of ammonia nitrogen in the raw wastewater that flows per day per 1 rn of filler material) On the other hand, the ammonia nitrogen filler surface area load is usually 001 to 5 far/rr?'day iJiα
Set within the range. In other words, with respect to the surface area load of the ammonia nitrogen filler, if it is less than 0.01 tr/rrI''·day, sufficient nitrification performance can be obtained, but the equipment becomes too large and the overall efficiency deteriorates, so that 5 f r/= 11 If the temperature exceeds 1 day, the nitrification performance decreases, and both are problematic and undesirable.

Furthermore, in order to perform the nitrification process efficiently, it is important to maintain the dissolved oxygen in the waste water at 11 PP+n or higher in the drainage channel of the Ij+ water in the nitrification process. or,
It is preferable to perform the treatment at a pH of about 6 to 9.

Next, the amount of circulating water of the nitrification process effluent to the mixing process is determined by the following (3 equations) depending on the desired nitrogen removal rate.

Circulating water amount: nQM/day =. . −□×Q・・・・・・(
3 formula) % formula %) () Next, the present invention will be explained in more detail with reference to Examples.

Example 1 After removing foreign substances from wastewater, mainly gray water, using a screen, BOD and nitrogen compounds in the wastewater were removed using an example of the treatment method based on the present invention shown in the process diagram of Fig. 1. The treatment was carried out as follows, and the results shown in Table 1 below were obtained.

That is, in the treatment method based on the method of the present invention described above, for the denitrification step in the first stage of the gravity flow type catalytic oxidation step, the water flow rate is set to about 2 to 3 m/min, and the total length of the filler in the waterway is The height was approximately 150m. As a filler, it has a specific surface area of 71 rn'/to' and a beam-to-beam ratio of 95 to 9.
A polyvinyl chloride packing plate having a corrugated pattern on 9% of the surface was filled.

Regarding the nitrification process at the latter stage of the gravity flow type catalytic oxidation process, the water flow rate was set at about 2 to 3 m/min, similar to the denitrification process, and the total length of the filler in the waterway was about 420 m. As the filling material, a polyvinyl chloride plug plate similar to that used in the denitrification process was used, except that the specific surface area was 129 m/nr. In addition, a step was provided in the middle of the water channel in the nitrification process for the purpose of oxygen replenishment, so that sufficient gas-liquid contact could be carried out by the falling of IJ water. It's ox.
The amount of circulating water from the nitrification step was adjusted to about 800-000% of the original drainage amount using a circulation pump in the pumping step.

Table 1 = Treatment results according to the treatment method of the present invention shown in Figure 1 Stone The wastewater is allowed to flow down into a waterway with a built-in filler without using the power of the Nodam, and at that time, dissolved oxygen in the wastewater is reduced to 1. By creating an area where the concentration is below PPm and maintaining the dissolved oxygen in the wastewater in the nitrification process above IPPm, the gravity flow type catalytic oxidation method efficiently removes BOD and nitrogen compounds from the wastewater at the same time. It is possible to achieve remarkable resource-saving and energy-saving effects.

In this example, no power is used for the circulation pump, but in some cases, even if power is used for supplementary aeration during the nitrification process, the features and effects of the present invention can still be achieved. is not impaired.

[Brief explanation of the drawing]

FIG. 1 is a process diagram of an example of the treatment method of the present invention. Qml/day...Raw wastewater volume, treated water volume, n...
......Circulation ratio, nQffl/[E]-...
... Circulating water volume. Patent applicant Mitsubishi Plastics Co., Ltd. Agent Patent attorney Tsunebe Ogawa

Claims (1)

[Claims] After introducing wastewater containing BOD substances and nitrogen compounds into a waterway incorporating a filler and allowing it to flow down, - the effluent from the end of the waterway is mixed with said wastewater and returned to said introduction part of said waterway; When circulating and forming a denitrification process and a nitrification process in the waterway to simultaneously remove B'OD substances and nitrogen compounds in the wastewater, the filler in the treatment process and the wastewater are brought into contact with each other. Using a gravity flow type catalytic oxidation method without using power for stirring and aeration of the oxygen supply tank, the dissolved oxygen in the wastewater in the drainage waterway of the denitrification process in the gravity flow type catalytic oxidation process is 1.PPm or less. 1. A wastewater treatment method, comprising: providing a region where the water is concentrated, and maintaining dissolved oxygen in wastewater at a level equal to or higher than L PPm in a drainage waterway of a nitrification step in a gravity contact acclimatization step.